Epstein-Barr virus (EBV) is a human herpesvirus that establishes a chronic carrier state in almost one hundred per cent of the population world-wide. It has considerable importance as a pathogen associated with infectious mononucleosis, oral hairy leukoplakia, Burkitt's lymphoma, immunoblastic lymphomas of the immunosuppressed, nasopharyngeal carcinoma, T cell malignancy and Hodgkin's disease. A current model of pathogenesis suggests that EBV replicates productively in epithelial tissue of the oropharynx and establishes latency in B lymphocytes. Virus then trafficks between the two cell types as it enters the body and is periodically shed in saliva of infected individuals. The long term objective of this work is to understand the first steps in infection of both target cells of EBV which are critical to spread of virus within and between hosts. The immediate goals of this application are to use recently developed techniques for deriving EBV mutants to investigate the roles of known or putative EBV envelope proteins in the process. The phenotypes of mutated virus will be examined in vitro in primary B lymphocytes and in an SV40 transformed epithelial cell line that has been transfected with the B cell receptor for EBV. Phenotypes of mutated viruses will be examined in vivo in CB. 17 scid/scid immunodeficient mice engrafted with human lymphoepithelial tissue. There are three specific aims. The first is to examine the effects of deleting expression of proteins in the gp85 complex on the ability of virus to penetrate cells. Additional point mutations in gp85 will be evaluated for their effects on the integrity of the complex using recombinant proteins expressed in isolation; those that do not interfere with complex formation will then be built into virus for further functional analyses. The second aim is to examine the phenotype of virus deleted for expression of gp110, the EBV homologue of HSV-gB. The third aim is to determine whether or not four remaining potential virion membrane proteins are essential for virus replication, and to examine the location of each that proves to be so.